1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling an on-off state of a cell and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, increases peak data rate and throughput, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), licensed-assisted access (LAA) using LTE, etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
The UE may need to monitor control channels of cells of the eNB, when the UE communicates with the eNB via the cells, i.e., carrier aggregation (CA) is supported. In certain situations, one or more of the cells may be turned off by the eNB, and the UE does not need to monitor the cell(s) which is turned off and power consumption of the UE can be reduced. The cell(s) which is turned off may be turned on again or a new cell may be turned on (i.e., added) to improve throughput of the UE. However, tens of milliseconds (e.g., 10-60 ms) are needed for switching on-off states of the cells via a higher layer signaling (i.e., network coordination time and/or media access control (MAC) delay). A transition time (i.e., delay) needed for switching the on-off states of the cells is great, and operations of the UE and the eNB are not efficient. Accordingly, throughput of the UE is degraded.
Thus, how to improve efficiency of the switching of the on-off state of the cell is an important problem to be solved.